Electrical breakdown device



Patented Mar. 7, 1950 UNITED STATES PATENT (JFFICE ELECTRICAL BREAKDOWNDEVICE Navy Application May 25, 1944, Serial No. 537,315

4 Claims.

This invention relates to radio transmitting and receiving systems inwhich a transmitter and receiver are operated on a single antenna incombination with an electrical breakdown discharge switch, such as thatdisclosed in the James L. Lawson application entitled Protection ofreceivers against overload, S. N. 479,662, filed March 18, 1943, andmore particularly to a means for assuring maximum protection to thereceiver against high powered inputs.

The protection afforded to the receiver of radio echo detection systemswhere such an electrical breakdown discharge switch is most commonlyused is not complete, since during the period that the radio echotransmitter is turned off and for a short period afterit is turned onthe discharge switch will not break down, for reasons hereinafteradvanced, thus rendering it incapable of protecting the receiver duringthese periods from pulses received from both nearby radio echo detectionsystems and the local transmitter itself.

It is thus an object of this invention to pro vide a manually operablemeans for improving the protection afforded receivers by an electricalbreakdown discharge switch of the foregoing type.

Other objects and features of the present invention will become apparentupon a careful consideration of the following detailed description whentaken together with the accompanying drawings the figures of whichrepresent a typical embodiment of the invention and are not to beconstrued as a definition of the limits of the invention. Reference forthe latter purpose is to be had to the appended claims.

Fig. l is a cross-sectional view taken through the axis of a typicalbreakdown discharge switch, showing a typical structural arrangement ofthe invention, and Fig. 2 is a portion of Fig. 1 broken away therefromand illustrating the additional protective effect lent to the receiverby the operation of the invention.

In order to facilitate an understanding of the function of the presentinvention, the operation of an electrical breakdown discharge switch ofthe type disclosed in the above mentioned appli cation of James L.Lawson will be here briefly reviewed. In the structural assembly, atoroidal or cylindrical cavity shown at In is provided, so dimensionedas to resonate at the frequency of operation. Disposed within the cavityat diametrically opposite points are input and output coupling loops,illustrated respectively at 22 and Il whereas at the central axis of thecavity is a spark gap 23 formed by a close approach of the 2 upper andlower walls 12 and it of the cavity in. Also provided is a keep aliveelectrode 24 which is held in close proximity to the spark gap at apotential negative with respect to the gap electrodes so as to produce asupply of ions around the gap thereby facilitating breakdown thereofwhenever a surge of power appears across the gap electrodes. The regionsurrounding the gap 23 is preferably maintained at a reduced pressure bythe sealed glass chamber 25. In practice, the breakdown switch isinterposed between the receiver and its junction to the maintransmission line which connects the transmitter to the antenna,preferably at a point a /4. wavelength from the receiver junction. Thuswhen the transmitter pulses, the energy of the system breaks down thespark gap thereby shorting the receiver line at the switch thusrefiecting a high impedance at the junction and hence inhibiting thetransfer of excessive energy to the receiver. If, however, the spark gapfails to ignite due to a momentary inoperativeness of the keep aliveelectrode, for example, a large quantity of energy Will be forced uponthe detector of the receiver (usually a crystal) causing great damagethereto. As previously mentioned this damage is most likely to occurduring the period that the transmitter is turned off and for a shortperiod after the inception of operation thereof. It is for this reasonthat the retractable shorting plunger M is provided, suitably adapted toshort the coupling loop ll to the wall l2 of the cavity, thereby causingequal and opposite currents a and b to be induced in the upper and lowerloops. These currents will cancel at the center conductor 55.Unfortunately the currents are not actually equal, but substantially so,so that attenuation up to db. will result. The amount of attenuation isan inverse function of the amount of resistance between the shortingplunger 14 and the adjacent surfaces of the wall l2. That is, thesmaller the resistance the greater the tendency to equalize currents atand b and hence the greater the attenuation. It is for this reason thatthe cylindrical choke type resonator i6 is provided, having at one end aconstricted portion ll adapted to open into the cavity it. and aninwardly extending tubular flange member H3 at the other end, into whichthe shorting plunger 14 is adapted to extend. The cavity I9 formed bythe plunger M and the cylindrical member #6 is of such a dimension(preferably a /2 wavelength) that regardless of the degree of electricalcontact effected between the plunger M and the flange 18 at point 20,there Patented Mar. 7, 1950 UNITED STATES PATENT QFFICE ELECTRICALBREAKDOWN DEVICE Navy Application May 25, 1944, Serial N 0. 537,315

4 Claims.

This invention relates to radio transmitting and receiving systems inwhich a transmitter and receiver are operated on a single antenna incombination with an electrical breakdown discharge switch, such as thatdisclosed in the James L. Lawson application entitled Protection ofreceivers against overload, S. N. 479,662, filed March 18, 1943, andmore particularly to a means for assuring maximum protection to thereceiver against high powered inputs.

The protection afforded to the receiver of radio echo detection systemswhere such an electrical breakdown discharge switch is most commonlyused is not complete, since during the period that the radio echotransmitter is turned off and for a short period afterit is turned onthe discharge switch will not break down, for reasons hereinafteradvanced, thus rendering it incapable of protecting the receiver duringthese periods from pulses received from both nearby radio echo detectionsystems and the local transmitter itself.

It is thus an object of this invention to provide a manually operablemeans for improving the protection afforded receivers by an electricalbreakdown discharge switch of the foregoing type.

Other objects and features of the present invention will become apparentupon a careful consideration of the following detailed description whentaken together with the accompanying drawings the figures of whichrepresent a typical embodiment of the invention and are not to beconstrued as a definition of the limits of the invention. Reference forthe latter purpose is to be had to the appended claims.

Fig. 1 is a cross-sectional view taken through the axis of a typicalbreakdown discharge switch, showing a typical structural arrangement ofthe invention, and Fig. 2 is a portion of Fig. 1 broken away therefromand illustrating the additional protective effect lent to the receiverby the operation of the invention.

In order to facilitate an understanding of the function of the presentinvention, the operation of an electrical breakdown discharge switch ofthe type disclosed in the above mentioned application of James L. Lawsonwill be here briefly reviewed. In the structural assembly, a toroidal orcylindrical cavity shown at I is provided, so dimensioned as to resonateat the frequency of operation. Disposed within the cavity atdiametrically opposite points are input and output coupling loops,illustrated respectively at 22 and H whereas at the central axis of thecavity is a spark gap 23 formed by a close approach of the upper andlower walls 12 and [3 of the cavity Hl. Also provided is a keep aliveelectrode 24 which is held in close proximity to the spark gap at apotential negative with respect to the gap electrodes so as to produce asupply of ions around the gap thereby facilitating breakdown thereofwhenever a surge of power appears across the gap electrodes. The regionsurrounding the gap 23 is preferably maintained at a reduced pressure bythe sealed glass chamber 25. In practice, the breakdown switch isinterposed between the receiver and its junction to the maintransmission line which connects the transmitter to the antenna,preferably at a point a /4, wave length from the receiver junction. Thuswhen the transmitter pulses, the energy of the system breaks down thespark gap thereby shorting the receiver line at the switch thusreflecting a high impedance at the junction and hence inhibiting thetransfer of excessive energy to the receiver. If, however, the spark gapfails to ignite due to a momentary inoperativeness of the keep aliveelectrode, for example, a large quantity of energy will be forced uponthe detector of the receiver (usually a crystal) causing great damagethereto. As previously mentioned this damage is most likely to occurduring the period that the transmitter is turned off and for a shortperiod after the inception of operation thereof. It is for this reasonthat the retractable shorting plunger M is provided, suitably adapted toshort the coupling loop H to the wall [2 of the cavity, thereby causingequal and opposite currents at and b to be induced in the up per andlower loops. These currents will cancel at the center conductor l5.Unfortunately the currents are not actually equal, but substantially so,so that attenuation up to db. will result. The amount of attenuation isan inverse function of the amount of resistance between the shortingplunger 14 and the adjacent surfaces of the wall l2. That is, thesmaller the resistance the greater the tendency to equalize currents aand b and hence the greater the attenuation. It is for this reason thatthe cylindrical choke type resonator i6 is provided, having at one end aconstricted portion ll adapted to open into the cavity 19, and aninwardly extending tubular flange member l8 at the other end, into whichthe shorting plunger I l is adapted to extend. The cavity l9 formed bythe plunger M and the cylindrical member it is of such a dimension(preferably a wavelength) that regardless of the degree of electricalcontact effected between the plunger M and the flange I8 at point 20,there

